Apparatus for use in aligning wheels of automotive vehicles are found to make measurements of four wheel alignment angles of caster, camber, K.P.I. (steering axis inclination), toe and track of the rear wheel.
Caster requires that measurements be made at a right angle to the wheel assembly and that a vertical reference be established, referencing the center assembly and that a vertical reference be established, referencing the center line of the king-pin or steering support arm to true vertical. The calculated values in degrees or fractions thereof between the two vertical planes will be the caster angle. The caster angle is commonly defined as the forward or backward tilt of the king-pin or steering support arm at the top.
Camber requires that measurement be made at a right angle to the wheel assembly and requires that a vertical reference be established, referencing the center line of the wheel assembly to true vertical. The true value in degrees or fractions thereof between the two vertical planes will be the true camber angle. The camber angle is commonly referred to as the inward or outward tilt of the wheel.
K.P.I. (king-pin or steering axis inclination) requires that measurement be made parallel to the wheel assembly and requires that a vertical reference be established referencing the center line of the king-pin or steering support assembly to true vertical, this value plus or minus the camber angle will be the calculated angle of K.P.I.
Toe requires that measurement be made to determine the parallelism, or deviation from parallel, of opposed wheels of a vehicle, either the steerable wheels, the rear wheels or both.
Tracking requires that measurement be made to determine the parallelism of all four wheels of a vehicle. The front and rear wheels of one side of the vehicle referenced to the center line of the vehicle and compared to the opposed wheels. All four wheels should track in a straight ahead position.
There are many prior art devices for measuring the angles of caster, camber and K.P.I., most devices utilize gravity seeking sensors to determine or measure departure of this reference from horizontal. Early devices used a pendulum or plum-bob with a pointer attached thereto that is referenced to a scale or chart as it departed from vertical. Martin U.S. Pat. No. 2,177,669 discloses a spirit level device for measuring camber and caster angles; MacMillan U.S. Pat. No. 2,765,540 shows an arrangement for measuring such angles with a pendulum and a variable inductive magnetic coupling arrangement; Holaday U.S. Pat. No. 2,603,881 discloses another approach which utilizes relative movement between various reference components for varying electrical resistances to determine these values; Butler U.S. Pat. No. 3,913,236 shows two gravity sensing electrolytic transducers connected in an electrical resistance bridge circuit that provides for remote readout when the selected transducer is tilted to or away from a horizontal.
Prior devices such as described above have mainly been used to measure angles of caster and camber only. Other arrangements which were designed to provide types of readout, either locally or remotely have been relatively limited, cumbersome, complex, expensive and difficult to maintain and keep in calibration.